Method and apparatus for controlling torch spacing



Dec. 19, 1950 e. M. DEYMING 2,534,958

' METHOD AND APPARATUS FOR CONTROLLING TORCH SPACING Filed Jan. 14, 1947 FIG.I

AC SUPPLY a system such as that disclosed in the UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR CON- TROLLING TORCH SPACING George M. Deming, deceased, late of Orange, N. 5., by Leonard G. Brown, administrator, South Orange, N. 3., assignor to Air Reduction Company, Incorporated, a

York

corporation of New Application January 14, 1947, Serial No. 721,891

7 y This invention relates to a method and apparatus for controlling the spacing between the tipof a gas torch and the surface of a Work- .piece that is being cut, welded, or otherwise acted upon by the torch.

' In mechanical cutting, welding, or heat-treating apparatus it is desirable to maintain the tip of the gas torch a substantially constant distance from the work-piece regardless of irregu- 'larities in the work surface. Various means have been proposed for accomplishing this, such as a guide roller that runs on the work surface and supports the torch, or an electrical system for automatically maintaining the torch spacing constant.

One electrical system for this purpose is disclosed in the patent to Chester Mott et al. No. 2,364,645, issued December 12, 1944. The present invention is an improvement on the method and apparatus of that patent.

A torch flame is electrically conductive, and assuming other factors remain constant, the conductivity of the flame decreases with increase in the length of the flame and'vice versa. In

the method of the Mott et a1. patent the change in conductivity of the flame caused by its change in length when the torch spacing departs from the desired normal is made use of to automaticallymaintain the torch spacing substantially con- 's'tant. An electric current is passed through the torch flame and between the torch tip and the work surface and the torch is automatically moved toward and away from the work surface in accordance with changes in the conductivity of the flame to keep the spacing of the torch tip substantially at the desired normal.

above stated, the conductivity of a torch -'flame'varies inversely with its length only if other factors remain constant. There are many factors that can affect the conductivity of the name such as the ratio of the gas mixture that feeds the flame and the diameter of the flame "provide an electrical system for controlling torch 's'pacing that operates on the same general principle as that disclosed in the Mott et a1. patent but which is more practical.

- Another object is to provide an improved methed and apparatus for automatically maintaining the sp'acing'between a gas torch and the workpiece at a substantially constant predetermined 3 Claims. (Cl. .148-9) value regardless of irregularities in the work surface. i

A further object is to provide a method 0 automatically maintaining substantially constant torch spacin by utilizing the conductivity of the \orch flame and in which the influence on the ,onductivity of the flame of the factors other than the length of the flame are rendered negligible or are greatly insubordinated to the influence that the length has on the flame conductivity.

According to the invention an electron emissive element, or electrode, is placed in the torch flame to emit electrons when heated by the flame and thus reduce the electrical resistance of the dance. The electrode is preferably made of tungsten, but any other material that emits electrons readily when at an elevated temperature, and

that can withstand the flame temperature, is satisfactor for the electrode. Theconductivity of the flame itself is relied upon to complete an electric circuit from the electrode to the work and the torch is automatically moved toward and away from the work surface in accordance with variations in the conductivity of the flame caused by changes in its length as the torch spacing de parts from the desired normal. However, as explained above, it is difficult to maintain the conductivity of the flame constant for a given torch spacing. By using the tungsten electrode the resistance between the electrode and work for a given spacing is greatly reduced. The low resistance path supplied by the electrons emitted from the electrode ma be considered the equivalent of a low resistance (r) in parallel with the resistance of the flame (R), a high resistance. In a two-branch parallel electric circuit the equivalent resistance RT is expressed b where R and 1' represent the resistances of the individual branches. 'From this it is obvious that if R is considerably larger than 7", RT approaches 1', and large variations in R, have little effect on Therefore, for any given torch spacing the variations in the resistance of the flame caused by gas proportions, flame diameter, etc., become negligible. Thus the overall resistance between the torch and the work is affected very little except by the spacing and now may be reliably used to control torch spacing.

The improved method, and apparatus embodying the invention and that is 'suitable for use in carrying out the method, are illustrated in the accompanying drawing, in which:

Figure 1 is a simplified schematic diagram of a system embodying the invention; and

Fig. 2 is a perspective view of an apparatus embodying the invention.

Referring to Fig. 1, a gas heating or cutting torch H is shown in operating position above a work-piece 12. A bracket I3 near the lower end of the torch ll supports a tungsten rod 14 that extends into the path of the flame from the torch. The work-piece I2 is grounded. The bracket I3 is connected by aconductor I5 to'one side of two potentiometers l8 :and I9 connected in parallel with each other. The other side of the parallel potentiometers is connected to the negative terminal of a battery 1601 other source of electric potential. The positive terminal of the battery I6 is grounded, completing the circuit to the work-piece l2. A variable tap on the potentiometer 18 is connected to a resistance 29 which is connected in series with the control grid of a Thyratron tube. 2|. A. variable tap of the potentiometer I9 is similarly connected in series with a resistance 22 and the control grid of a Thyratron tube 23. The Thyratron filaments are supplied by a separate secondary filament winding on a transformer 24. The screen grids of the Thyratrons are grounded with the cathodes. The Thyratron plates are connected in series with relays and 25 and a high voltage secondary of thetransformer 24 as shown. The leads from the transformer primary are placed across 'an A. C. supply. The high voltage secondary is center tapped to ground.

A series, split-field, reversing motor 21 has field windings 28 and 29. One side of the motor armature winding is connected 'to one side of a power line. The other side of the motor has two leads, one from each field winding. Field winding 28 is connected to'a relay contact 25a in series with a relay contact 28a and the opposite side of the power line. Field winding 29 is connected to a relay contact 25?) in series witha relay contact 26b and the opposite side of the power line. Re-

lay contacts 25a and 26a are normally closed, and contacts 251) and 261) are normally open.

Fig. '2 illustrates apparatus-embodying the invention and having the torch l I supported by an adjustable bracket 28 on a bar 29 of a folding parallelogram universal cutting machine. The electronic control circuits are enclosed in a housing The motor 21 is connected through reduction gears to a pinion engaging the'rack 3| on the torch.

When the torch II is lit, the tungsten rod [4, in the path of the flame, is heated and emits electrons. Current then flows from the battery l6 (Fig. 1) through .the parallel potentiometers l8 and [9, through the conductor l5, bracket I3, the tungsten rod M, the flame, and the workpiece E2 to ground, completing the circuit to the positive side of the battery It. The settings of "the variable taps on the potentiometers l8 and I9 are negative with respect to ground. The cathodes of the Thyratrons are grounded. Then when plate voltage is applied to the Thyr-atrons by the high voltage secondary of the transformer '24 the tubes can be rendered conductive or nonconductive by the settings of thepotentiometers. The currentxpath when a'tube 21 or 23 is fired is .from ground, through the tube, through therelay 25 or 26, through one half of the transformer high voltage secondary, and out the center tap thereof .to ground.

Potentiometer I8 is set to keep the tube 2| cut off when the torch is properly spaced. Potentiometer i9 is set to keep the tube 23 firing. Under these conditions relay 25 is de-energized, contact 25a is closed and.25b is open. Relay 25 is energized, contact 2Gais open and 26bis closed.

Thus the a motor circuit is open at 26a and the b circuit is open at 251) and the motor is de-energized.

When the torch spacing increases, the resistance of the torch flame between the tungsten rod [4 .and the work-piece l2 increases, and the potentials at the potentiometer taps become more negative with respect to ground. This has .no effect on tube 2| which remains cut on", nor

on relay 25. However, tube 23 is cut off by the change in potential, relay 26 is de-energized, contact 26a is closed, and contact 261: is opened. The b motor circuit is now open at 25b and 26b. The a motor circuit is now closed allowing current to flow through field winding 28 of the motor 21 causing rotation of the motor in .a .dimotion to move the torch toward the work-piece and restore the optimum spacing.

When the torch spacing becomes less than the optimum, the grids of the tubes .become less negative, both tubes fire and both .relays .are en- .ergized. This opens the a. motor circuit at 25c and 25a and closes the b motor circuit through field winding 29 causing corrective rotation oppmlte to the above.

"be controlled. This practically eliminates or renders negligible the effect on the flame :conductivity of all variable other than the distancebetween the torch tip and the work-piece, and therefore makes an electrical control system of the kind described entirely practical and reliable.

It is claimed:

l. The method of controlling the spacing .of a torch tip from the surface of awork-piecewhich comprises positioning an electron emissive element in fixed relation to the torch tip and in the torch flame so that when heated by the fiame it will emit electrons, passing an electric current through the flame and between said element and the work so that an electron stream is produced between said element and the work which lowers the electrical resistance of the portion .of the flame between the electron emissive element and the work, and moving the torch tip toward and away from the work surface in accordance with changes in the electrical conductivity of said portion of the fiame.

2. The method of controlling the spacing of a torch tip from the surface of a work-piece which comprises mounting an electron emissive element on the torch so that a'portion of it projects into the torch flame and will be heated thereby to cause electrons to be emitted, passing an electric current through the fiame and between said .element and. the work so that an electron stream produced between said element and the work toward and away from the work surface .in accordance with changes in theelectrical conduc- 'tivity ofrsaid portion of the flame.

3. Apparatus for controlling the spacing of a torch tip from the surface of a Work-piece comprising electrically-actuated means for moving the torch tip towards and awa from the workpiece, an element adapted to emit electrons when heated, means for supporting saidelement from the torch so that a portion of it projects into the flame from the torch and will be heated there by, means for passing an electric current through a flame from the torch and between said element and the work-piece, and electrical control means responsive to a variance of the resistance between the electron-emissive element and the work-piece for causing operation of the electrically-actuated means.

LEONARD G. BROWN, Administrator of the Estate of George M Deming,

Deceased.

REFERENCES CITED fhe ioilowing references are of record in the file of this patent:

UNITED STATES PATENTS Numoer Name Date 2,127,977 Lamb -1 Aug. 23, 1938 2,364,645 Mott et a1 Dec. 12, 1944 2,411,737 Klinke Nov. 26, 1946 2,438,344 Meincke Mar. 23, 19 18 

